We have developed a nice form add-in for Outlook Appointment Items which shows the location of the meeting on graphical map. The question is whether it is possible to add a button to the standard calendar reminder popup. The typical example is the Skype plugin, which shows "join online" button, if the calendar entry contains a Skype link:
A small example in C# would be enough, unfortunately i cannot find an API reference which would support it
There is no public API to do that.